Method of plating iron with aluminum and product of such method



Patented F eb. 19, 1935 UNITED STATES,

PATENT OFFICE METHOD OF PLATING IRON WITH ALUMI- NUM AND PRODUCT OF SUCH METHOD Anton Wimmer, Dortmund, Germany 2 Claims.

When plating iron in the form of sheets or bands with aluminum or aluminum alloys according to any of the known methods, the further working of the material so as to transform 5 it into drawn bodies and pressed bodies necessitates making the plated iron soft by glowing it. Experience has found that when this procedure is followed, the plated iron shows spots after it has been glowed. It has now been discovered surprisingly that the formation of the spots depends upon the composition of the aluminum, as well as of the iron employed. In this connection it is surprising that pure aluminum, even very pure aluminum, tends very strongly to form spots, even though the use of aluminum is of great advantage because it is not easily corroded. It is also true that pure iron, that is, any well oxidized iron, will tend very strongly to cause spotting. Moreover, commercial types of aluminumcan not generally be used for the purpose in view. The spots are, for instance, particularly strong if the aluminum has a certain content of magnesium. It is also noted that aluminum alloys and the low-grade commercial.

aluminum types are subject to corrosion in a higher degree than is pure aluminum. The spots above referred to are due to the formation of an iron-aluminum alloy when the iron thus plated with aluminum is subsequently heated to a temperature at which it becomes soft, that is, a temperature of about 520 C. Such heating of the plated iron in order to soften it is resorted to in various operations, for instance when the plated iron is to be subjected to a deep-drawing process. The iron-aluminum alloy is brittle and therefore very liable to crack and to separate from, or peel ofi, the underlying metal. In my invention, I avoid the formation of this alloy and obtain a product which can be bent or deformed without breaking the connection between the iron and its plating. The principle of my present invention consists in applying aluminum to iron under conditions which prevent the formation of spots when the iron thus plated is subsequently heated to a temperature at which it becomes soft.

Now, according to the present invention, the arising of spots .during the subsequent glowing or heating procedure in order to make the material soft can be obviated either by the employment of a pure aluminum to which from .2 to 15% of silicon has been added, or by the use of a known type of iron having a content of oxygen of from .03 to .15%. The oxygen content is in these cases ascertained according to the method disclosed'in the manual or textbook of Bauer-Deiss entitled Probeentnahme und Analyse von Eisen und Stahl, 2nd edition, 1922, page 288, the statements made therein having later on been corrected by Oberhoffer and Keutmann in an article published in the periodical Stahl und Eisen, volume (1925), page 1557 (addition of antimony) and volume 46 (1926), page 1045 (lumps instead of millings).

The progress attained by the use of such types of aluminum or of iron as stated in the preceding paragraph will now be made clear with the aid of an example, as follows: The aluminumplated sheet-iron that has been hardened by cold rolling must vthereafter be made soft by glowing. With the most suited qualities of iron the requisite temperature does not lie below 520 C. If the iron is plated with pure aluminum having a content of .09% of silicon, the spots will form at a temperature of about 450 C. It is impossible to obtain with this aluminum an aluminumplated article that has no spots when it is heated to that temperature at which the iron becomes soft. The temperature at which spots arise must, at all events, be a little higher than the recrystallization temperature. When aluminum with .2% of silicon is used, the spots begin to appear at about 530 C. This percentage is, thus, the

lowest content of silicon in an aluminum suited for plating and which permits the plated article to be glowed soft without forming spots. But it must be observed that the range of temperature between the recrystallization and the formation of the spots is only very small and can be used only with very great precaution. With a content of .6% of silicon in the aluminum the formation of spots arises only at about 580 C. With this temperature range which has now been attained the glow temperature may be increased to such a degree that the interior of aluminumplated iron articles placed in a kiln for not too long a period will reach the recrystallization temperature of the iron, that is, will become soft, while at the same time the temperature of the outer surface of the article will not exceed the temperature at which spots begin to appear. The addition of silicon facilitates, therefore, considerably the work and decreases likewise considerably the Waste.

In order to make matters still more clear, I amv adding some more explanatory remarks:

There is also a certain relationship between the temperature and the amount of silicon used. Certain temperatures require a greater amount of silicon before the formation of spots could be avoided. The temperature used must be so chosen that the iron will certainly be glown soft, and the amount of silicon should vary in accordance with this temperature. Thus, glowing the material in such a manner that no spots arise can be carried out also with a smaller quantity of silicon, but in this case the iron will not beplating adheres firmly to the iron and no black spots arise when the plated iron has been heated to 520 C., that will indicate that the requisite excess 01' oxygen according to this invention exists in the iron.

My present application is a division oi. my earlier application filed in the United States Patent Oflice on March so, 1933, Serial so. assess which has matured into Patent No. 1,982,563,

dated November 27, 1934. In said application I have claimed that species otmy invention according to which the desired results are obtained by applying to iron, aluminum containing from .2 to 15% or silicon, and said species is therefore not claimed in the present application.

I claim: 1 I

1. The method 01 plating iron'with aluminum which consists in applying aluminum to iron containing from .03 to .15% 0! oxygen, whereby the resulting plated iron can be heated to a temperature at which it becomes soft, without the formation of spots.

2. A metal article capable of being heated to a temperature, at which iron becomes soft without spotting, comprising a. base member of iron superimposed plating layer' or aluminum.

' ANTON containing irom'.03 to .15% of oxygen, and a 

